JPH01134429A - Electrochromic display device - Google Patents

Abstract

PURPOSE:To increase response speed and to prevent deterioration of the thin film of an electrochromic material by adding plural acid base indicators which are different in coloration pH region as an acid base indicator and controlling the electricity passing between both electrodes, thereby controlling the indicators so that one or plural indicators among the indicators form colors. CONSTITUTION:An aq. electrolyte soln. prepd. by adjusting the pH of a 1mol./l aq. soln. of sodium sulfate by sulfuric acid to 6.0 is injected into a 1st cell 3a and a 2nd cell 3b. Furthermore, the plural acid base indicators which are different in, for example, the discoloration pH region and are different in coloration are compounded in such a manner that the coloration is successively changed by the pH near the electrodes and such indicators are added as the plural acid base indicators of the different discoloration pH regions into the electrolyte soln. in the 1st cell 3a. A positive voltage and negative voltage are then alternately impressed at prescribed duty ratios between both electrodes 4a and 4b from an external power supply and the pH near the electrodes 4a, 4b is controlled by controlling the current values thereof, by which the coloration is controlled. The response speed is thereby increased and the deterioration of the electrochromic material is obviated. The high durability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrochromic display device, and particularly to an electrochromic display device that utilizes an acid-base reaction.

[Prior Art] Conventional electrochromic display devices include electrodes on which a thin film of electrochromic material that exhibits reversible color changes due to electrochemical reactions and other electrodes are placed in an electrolyte solution, and the direction of current flow is controlled. There are some that can be controlled to change color. The above-mentioned electrochromic materials include tungsten oxide (WOa),
Iridium hydroxide (Ir(OH)x), titanium oxide (
Ti0z>, molybdenum oxide (MOO3), etc., and these are formed into thin films on the electrodes by vapor deposition, sputtering, ion blating, etc. Furthermore, organic pigments include rare earth sifthalodianine, TTF polystyrene, viologen, and other pigments, which are formed into thin films on electrodes by coating, electrolytic formation, and the like.

[Problems to be Solved by the Invention] The color change in the conventional electrochromic display device described above is an electrochemical reaction, and is an interfacial reaction between a solid phase and a solid phase, or more specifically, an interfacial reaction between a liquid phase and a solid phase. The speed is slow and there are problems with the responsiveness of color changes.

There is also the problem that the thin film of the electrochromic material formed on the electrode deteriorates due to gas generation accompanying the electrochemical reaction. In general, it is not possible to achieve full color with one electrochromic display device. For example, when displaying full color in a display device, multiple colors that produce red, yellow, and blue or red, green, and blue are used. There is also the problem that the electrochromic display devices must be arranged adjacent to each other and the color development of each electrochromic display device must be controlled, making the device complicated.

Therefore, the present invention aims to solve the above problems and adopts the following configuration.

[Means for Solving the Problems] That is, the gist of the present invention is to arrange at least two electrodes sandwiching an electrolyte solution containing an acid-base indicator, and apply a voltage between the two electrodes from an external power source. , an electrochromic display device that controls color development of an indicator by controlling the direction of electricity flow between the two electrodes, wherein a plurality of acid-base indicators having different color change PL-1 regions are added as the acid-base indicator, An electrochromic display device is characterized in that electricity flowing between the indicators is controlled so that one or more of the indicators develops a color.

[Operation] A voltage higher than the theoretical decomposition voltage of water is applied between the two electrodes placed with the electrolyte solution in between. On the surface of the above two poles,
When electrolysis of water occurs and the pH of the electrolyte aqueous solution is <<7, the following reaction occurs at the anode: HzO → 1/202+28 +2e-...■ Cathode: 2H+2e-→H2...■ The pH of the electrolyte aqueous solution increases If >>7, anode: 20H-)H20+1/202 +2e...■ Cathode: 2H20+28--1-12+208- =■
reaction occurs.

As shown in equations (1) to (0) above, the reaction on the anode and cathode differs depending on the pH of the electrolyte aqueous solution, but in either case, the pH decreases near the anode and increases near the cathode.

Here, as a plurality of acid-base indicators with different color change pH ranges, for example, a plurality of acid-base indicators with different color change pH ranges and different color development may be mixed so that the color development changes sequentially depending on the pI-1 near the electrode. Add into electrolyte solution. Next, color development is controlled by controlling the pH in the vicinity of each electrode to a predetermined pH by alternately applying a positive voltage and a negative voltage at a predetermined duty ratio between the two electrodes from an external power source and controlling the current value.

[Example] Next, an example of the present invention will be described. The present invention is not limited to these, but includes various embodiments without departing from the gist thereof.

FIG. 1 shows a block diagram of essential parts of an electrochromic display device according to a first embodiment of the present invention.

The electrochromic display device of this embodiment has a configuration as shown in FIG. That is, the transparent glass substrate 1a, I
cell 1, the above-mentioned glass substrates 1a, 1
A transparent cell made of a fluorocarbon resin having a sulfone group is disposed between the cells 1 and 2 and partitions the cell 1 into a first cell 3a, which is a partition on the glass substrate 1a side, and a second cell 3b, which is a partition on the glass substrate 1b side. cation exchange membrane 2, the first cell 3
Indium tin oxide (hereinafter referred to as ITO) tl, which is a transparent electrode provided on the surface of the glass substrate 1a in a'
14a and the glass substrate 1b in the second cell 3b.
A transparent ITO film 4b is provided on the surface of the transparent ITO film 4b. The ITOIIIs 4a and 4b are connected to an external power source (not shown) through terminals 5a and 5b.

In addition, a 1 mol/1 aqueous solution of sodium sulfate (NazSO4) was added to the first cell 3a and the second cell 3b.
2304), an aqueous electrolyte solution adjusted to pH 6.0 is injected. Roughly speaking, a plurality of acid-base indicators having different discoloration 1) H regions are added to the electrolyte aqueous solution in the first cell 3a in the following manner.

That is, for 100ml of ethanol, phenolphthalein 20±10mg, methyl red 40±i0mg
, 60 ± 10 mg of methyl yellow, 80 ± 20 mg of bromothymol blue, and 100 ± 20 mg of thymol blue were added, and the pH was adjusted to 6.0 with 0.1N sodium hydroxide (NaOH) and sulfuric acid (H2SO4). It is added to the electrolyte aqueous solution in the cell 3a.The acid-base indicator prepared above exhibits a yellow color in an initial state where no voltage is applied from an external power source (not shown).

Table 1 shows the relationship between color development and pH range. In addition, at a pH in the middle of the pHfil range shown in Table 1, it exhibits a color intermediate between the two corresponding colors, for example, at pH 4 to 5.5, it exhibits a color intermediate between red and yellow, such as vermilion, orange, yellow-orange, etc. Develops color.

Table 1 Next, the voltage and current values applied to the ITO film 4a from an external power source in order to control the pH range near the ITO film 4a shown in Table 1 above will be explained.

FIG. 2 shows a waveform diagram of a pulse voltage applied to the ITO film 4a in order to develop a desired color.

First, as shown in waveform O, if no voltage is applied, the IT
l)H near the O film 4a remains at 6.0, and the electrochromic display device exhibits a yellow color. Next, by applying a voltage whose voltage amplitude and its duty ratio are controlled to predetermined values as shown in waveforms C to 4, the value of the current flowing through the ITO film 4a within a unit time is controlled, and the ITO film 4a is
The DH near the TO film 4a is maintained within a predetermined range to achieve the color development shown in Table 1. Table 2 illustrates the relationship between the voltage amplitude, duty ratio, and color development.

Table 2 The above voltage amplitude (V) is determined by the distance between the electrodes (L) and the voltage drop (VIR) of the ion exchange membrane. In this example, L = 1.0 cm, and VIR = 0.5 V for cation exchange. Membrane 2 was used. Table 2 shows examples of red, yellow, green, and blue color development, but if a voltage controlled at a voltage amplitude and duty ratio intermediate between waveform 1 and waveform 2 is applied, a color intermediate between red and yellow will be developed. , and other neutral colors can be realized in the same way. For example, if you want to change the coloring to red after it has been colored red, change the applied voltage from waveform 1 to waveform 4.
You can change it to .

As explained above, in this embodiment, by applying a voltage having a predetermined voltage amplitude and duty ratio between the electrodes of the first cell 3a and the second cell 3b, red, yellow, green, blue and It is possible to generate intermediate colors, and full-color display can be easily performed without complicated control by combining multiple electrochromic display devices. In addition, since the first cell 3a and the second cell 3b are partitioned by the cation exchange membrane 2, the movement of charge when applying the above voltage is due to the reaction between sodium ions (Na) and the cation exchange membrane 2. is executed. Therefore, the first cell 3
Between a and the second cell 3b, hydrogen ions (H) and water v
Since there is no movement of t-group ions (OH-), the first cell 3a
The internal pH is maintained within a predetermined pH range, stable and clear color development can be obtained, and electrochromic display devices can be made thinner. Roughly speaking, even if the application of voltage is stopped after a certain color is developed, the first cell 3a and the second cell 3b are separated by the cation exchange membrane 2, so that the inside of the first cell 3a is The color development is maintained because the pH is maintained around the pH when the voltage is applied for a considerable period of time. With the memory function based on the above-mentioned operation, for example, when used for displaying still images, images can be displayed for a considerable period of time without rescanning. In addition, since the electrochromic display device of this example is composed of a cell with transparent glass substrates facing each other, a transparent electrode, and a transparent ion exchange membrane, it can also be used for transmissive products such as color filters and shutters. Available.

Next, a second embodiment will be explained. As shown in FIG. 3, the second embodiment has a configuration in which the cation exchange membrane 2 of the first embodiment is removed.

In this example, p-
Nitrophenol, quinoline blue, and phenolphthalein are added to an electrolyte solution adjusted to pH 6.0. The color change pH range of all of the above acid-base indicators is 7.0.
As above, it initially appears colorless. Here, when a pulse voltage is applied in the same way as in the first embodiment and the vicinity of the ITO film 4a is maintained at around p)-17,0, it becomes yellow, and the pH is 8,
, exhibits a green or blue color near O, and exhibits a red color at a pH of 10.0 or higher. Various other acid-base indicators can be used, for example, p-nitrophenol, hexamethoxy red, bromcresol green in combination with I
As I is lowered, the colors can be changed to yellow, blue, and red.

Although the embodiments of the present invention have been described above, the present invention is not limited to these, and various embodiments can be adopted without departing from the gist thereof.

For example, in the first embodiment, the ion exchange membrane does not need to be transparent in order to be used as a reflective electrochromic display device, and the electrodes in the section where no acid-base indicator is added do not need to be transparent. The electrode of the section where is added may be placed separated from the glass substrate by a predetermined distance,
In this case, the electrode does not need to be transparent either. In the second embodiment as well, the electrodes can be placed separated from the glass substrate by a predetermined distance. Further, the ion exchange membrane may be an anion exchange membrane. Furthermore, the electrolyte aqueous solution is not limited to a sodium sulfate (NazSOa) aqueous solution, and any electrolyte that is directly unrelated to pH changes may be used. Furthermore, as a plurality of acid-base indicators with different color change pH ranges, for example, 0-cresol phthalein may be added in place of phenolphthalein, and p-ethoxychrysoidine or α-naphthyl red may be added in place of methyl red. Methyl orange or dimethylaminoazobenzene may be blended in place of methyl yellow, quinoline blue may be blended in place of bromothymol blue, and p-xylenol blue may be blended in place of thymol blue. Various combinations are possible. In the second example as well, various combinations other than the exemplified combinations are possible, and the combinations of acid-base indicators shown in the first example may be used, and vice versa. Note that color development may be controlled by keeping the duty ratio at a predetermined value and changing the voltage amplitude.

Since the color change in the electrochromic display device of the present invention is caused by an acid-base reaction in the liquid phase, the response speed is fast, the electrochromic material does not deteriorate, and the durability is high.

Further, full color display can be easily performed with one electrochromic display device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main part of the first embodiment, FIG. 2 is a waveform diagram of the applied voltage, and FIG. 3 is a block diagram of the main part of the second embodiment. 1...Cell"1a, ib...Glass substrate 2...Cation exchange membrane 3a...First cell 3b...Second cell 4a, 4b・ITO membrane (electrode) 5a, 5b...・Terminal agent Patent attorney Tsutomu Sadatsu (and 1 other person) Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. At least two electrodes are arranged sandwiching an electrolyte solution containing an acid-base indicator, a voltage is applied between the two electrodes from an external power source, and the direction of electricity flow between the two electrodes is controlled, so that the indicator An electrochromic display device that controls color development of
A plurality of acid-base indicators having different color change pH ranges are added as the acid-base indicator, and electricity flowing between the two electrodes is controlled so that one or more of the indicators develops a color. Electrochromic display device. 2. The electrochromic display device according to claim 1, wherein at least one electrode is transparent or translucent.